The present invention relates to a light source apparatus having a plurality of light-emitting elements disposed in a line, a light irradiating apparatus provided with the light source apparatus, an image reading apparatus provided with the light irradiating apparatus, and an image forming apparatus provided with the image reading apparatus.
An image forming apparatus such as a copy machine or a facsimile machine is provided with an image reading apparatus in order to read an image of an original. This image reading apparatus is ordinarily configured with an original placement plate, an original pressing plate, an illumination unit (light irradiating apparatus), and a photoelectric converter.
Herein, the original placement plate is formed of a light-transmitting material, and has the function that an original is placed on a surface of the original placement plate. The original pressing plate has the function of pressing against the back face of the original that has been placed on the surface of the original placement plate.
The illumination unit has the function of, while moving along the original placement plate in a scanning direction, which is the direction orthogonal to the width direction of the original, irradiating the original with irradiating light in the width direction of the original, the irradiating light being passed through the original placement plate. The photoelectric converter has the function of converting reflected light (subject-reflected light) to an image signal, the reflected light being light that has been emitted by the illumination unit and reflected by the original.
Recently, in consideration of life and power consumption, a light source apparatus employing light-emitting diodes has been adopted as a light source in the illumination unit in the above image reading apparatus. As this light source apparatus employing light-emitting diodes, a light source apparatus has been proposed in which light-emitting diodes are disposed at intervals in a line on a substrate (for example, see FIG. 1 of JP 2003-257230A, referred to below as Patent Document 1).
The light source apparatus described in Patent Document 1 is a light source apparatus used in a liquid crystal display. In such a light source apparatus in which light-emitting diodes are disposed at intervals in a line on a substrate, irradiating light includes direct light that is directly emitted from the light-emitting diodes, and substrate-reflected light, which is light that is emitted from the light-emitting diode and reflected by the substrate. This sort of light source apparatus having a simple configuration is advantageous from the perspective of cost.
Incidentally, in the illumination unit (light irradiating apparatus) of the above image reading apparatus, in the light source apparatus using light-emitting diodes as a light source, ordinarily, the light-emitting diodes are arranged in a single line at a certain interval. Therefore, there is a tendency for brightness unevenness to occur in the light with which the original is irradiated.
However, in the illumination unit of the above image reading apparatus, in order to increase the accuracy of reading an image of an original, it is effective to reduce the brightness unevenness of the light with which the original is irradiated as much as possible. As described above, in the light source apparatus as described in Patent Document 1 in which light-emitting diodes are disposed at intervals in a line on the substrate, the irradiating light includes direct light that is directly emitted from the light-emitting diodes, and substrate-reflected light, which is light that is emitted from the light-emitting diode and reflected by the substrate.
Therefore, for example, in the above light source apparatus described in Patent Document 1, a scheme is implemented in which substrate-reflected light, which is light emitted from the light-emitting diodes and reflected by the substrate, is suppressed. More specifically, on a forward side from the light-emitting face of the light-emitting diodes in the surface of the substrate where the light-emitting diodes are installed, a black area is formed that extends forward from the lower edge of this light-emitting face with a wider width than the width of the light-emitting face.
In the light source apparatus described in Patent Document 1, the black area is formed wider than the width of the light-emitting face of the light-emitting diodes. Therefore, as a result, substrate-reflected light that is reflected by the substrate is suppressed, but by suppressing the substrate-reflected light, merely the amount of light that is reflected is reduced, and so it is conceivable that the effect of suppressing light brightness unevenness is small.